254 HEAD AND NECK 



Arteria Mammaria Interna. The internal mammary artery 

 springs from the lower and anterior aspect of the subclavian, 

 directly below the thyreo-cervical trunk. It passes downwards 

 upon the anterior surface of the pleura, posterior to the medial 

 end of the clavicle and the medial end of the subclavian vein, 

 to reach the thorax. As it lies posterior to the subclavian 

 vein the phrenic nerve passes from the lateral to the medial 

 side, either anterior or posterior to it. In the neck the in- 

 ternal mammary artery is not accompanied by a vein. 



Truncus Costocervicalis. This branch takes origin from 

 the posterior aspect of the second portion of the subclavian 

 artery, close to the medial border of the scalenus anterior. 

 On the left side, however, it proceeds, as a rule, from the 

 first part of the parent trunk. To bring it into view the 

 subclavian artery must be dislodged from its position. It 

 is a short trunk which passes upwards and posteriorly over 

 the apex of the pleura to the neck of the first rib, where it 

 divides into the deep cervical artery and the superior intercostal 

 artery. 



If the lung is removed from the thorax the dissector 

 should take the opportunity of examining this artery from the 

 thoracic aspect. 



Arteria Cervicalis Profunda. This branch passes dorsally 

 and disappears from view between the transverse process of 

 the seventh cervical vertebra and the neck of the first rib. 

 It has been already noticed in the dissection of the back 

 of the neck (p. 173). 



The deep cervical vein is a large vessel. It joins the 

 vertebral vein. 



Arteria Intercostalis Suprema. The superior intercostal 

 artery turns downwards anterior to the neck of the first rib, 

 between the first thoracic nerve and the first thoracic ganglion 

 of the sympathetic. It gives a posterior intercostal branch to 

 the first space and ends as the posterior intercostal artery of 

 the second space (Fig. 5). 



Vena Subclavia. The subclavian vein is the continuation 

 of the axillary vein into the root of the neck. It begins 

 at the outer border of the first rib, and arches medially 

 on the anterior surface of the lower end of the scalenus 

 anterior. At the medial margin of this muscle, and posterior 

 to the sternal end of the clavicle, it joins with the internal 

 jugular to form the innominate vein. In connection with 



